debris formed because of the wear. The Al2O3-coated
specimen had a wear mechanism on the surface in the
form of flaky micro-cracks. This could be attributed to
the high hardness values of the specimens. Micro-cracks
occur if a critical value is exceeded in loading and
abrasive wear also takes place in relation to the fracture
toughness of the abraded material. The TiO2-coated
specimen showed that the wear mechanism on the
surface formed micro-cutting of various widths along
with plastic deformation because of micro crackings.
Figure 9g reveals that the transfer of the materials that
occurred from the pin to the disc. The debris produced
throughout the test was deposited on both sides of the
wear track. Over the wear track a few patches of the
initial surface are observed, indicating that the trans-
ferred steel film was detached as a result of a fatigue
process.
4 CONCLUSIONS
The AISI 1040 forged steel substrate was coated with
alumina, titania, chromia individually and again with
different combinations of ceramic oxides such as 45 %
Al2O3 + 55 % TiO2, 55 % Al2O3 + 45 % Cr2O3, and 45 %
TiO2 + 55 % Cr2O3 by using a plasma-spraying process
with an intermediate bond coat of NiCr, SEM tests were
carried out to determine the surface roughness and
adhesion of the coating onto the AISI 1040 substrate.
The specimen coated with 99 % Cr2O3 has higher
microhardness values among all the ceramic-oxide-
coated specimens, which was followed by 99 % Al2O3,
45 % TiO2 + 55 % Cr2O3, 55 % Al2O3 + 45 % Cr2O3. The
lowest hardness value was obtained from the ceramic
oxide coating surface with a mixture proportion of 45 %
Al2O3 + 55 % TiO2.
The chromia-coated specimen showed excellent wear
property when compared to other coating materials due
to its excellent adhesion to the base metal.
The increase in the weight percentage of TiO2 in the
Al2O3 ceramic material affects the microhardness value
of the specimens in a decreasing manner.
The microhardness values of the coated specimens
influence the wear loss. The specimens having higher
microhardness also have a higher wear resistance and
cause less wear loss.
If the weight percentage of TiO2 in Cr2O3 ceramic
materials increases, this decreases the microhardness
value of the specimens.
From the experimental results it can be concluded
that the pure 99 % Cr2O3 coated AISI 1040 forged steel
specimen showed better wear resistance property due to
dense, compact, defects free and good adhesion charac-
teristics, while compared to other coating materials.
Hence, it is recommended for surface coating on the top
mill roll shafts used in sugarcane industries to increase
the wear resistance of the shaft.
Acknowledgement
The research work was supported by my father Mr.
D. Ponnusamy and my spouse Mrs B. Malathi. Special
thanks to Professor Dr. K. K. Ramasamy and Dr. M.
Premkumar from Paavai Engineering College, Nama-
kkal, India, for their valuable help.
5 REFERENCES
1 S.-H. Yao, Comparative study on wear performance of traditional
and nano structured Al2O3-13 wt.% TiO2 air plasma spray coatings, J.
Ceram. Silikaty, 59 (2015) 1, 59–63
2 Y. Sert, N. Toplan, Tribological behaviour of a plasma – sprayed
Al2O3-TiO2-Cr2O3 coating, Mater. Technol., 47 (2013) 2, 181–183
3 C. A. Berkath, A. Khan, Dr. Anilkumar, P. M. Suresh, Tribological
behaviour of a plasma – sprayed Al2O3-TiO2 coating on Al-6082T6
substrate, Int. J. of Inno. Res. in Sci., Eng. and Techno., 3 (2014) 6,
13956–13963
4 M. H. Korkut, Y. Kucuk, A. C. Karaoglanl, A. Erdogan, Y. Er, M. S.
Gok, Effect of the abrasive grit size on the wear behaviour of
ceramic coatings during a micro-abrasion test, Mater. Technol., 47
(2013) 6, 695–699
5 S. Islak, S. Buytoz, I. Somunkiran, E. Ersoz, N. Tosun, N. Orhan, J.
Stokes, M. Saleem Hashmi, Effect on microstructure of TiO2 rate in
Al2O3-TiO2 composite coating produced using plasma spray method,
Optoelectro. Adv. Mater. – Rapid Comm., 6 (2012) 9–10, 844–849
6 S. Salman, R. Kose, L. Urtekin, F. Findik, An investigation of
different ceramic coating thermal properties, Mater. Des., 27 (2006)
7, 585–590, doi:10.1016/j.matdes.2004.12.010
7 M. S. Kumar, S. Natarajan, Analysis of tribological factors on dry
sliding wear behaviour of thermally sprayed carbide and ceramic
coatings by taguchi method, Int. J. of Eng. Sci. Tech., 3 (2011) 4,
3336–3347
8 G. Bolelli, V. Cannillo, L. Lusvarghi, T. Manfredini, Wear behaviour
of thermally sprayed ceramic oxide coatings, Wear, 261 (2006),
1298–1315, doi:10.1016/j.wear. 2006.03.023
9 A. Prasad, D. Gupta, M. R. Sankar, A. N. Reddy, Experimental
investigations of Ni/La2O3 composite micro-cladding on AISI 1040
steel through microwave irradiation, 5th Int. & 26th All India
Manufacturing Techno., Des. and Res. Conference, 2014, 55–61
10 M. S. Gok, The effect of different ceramics on the abrasive wear
behavior of coating surface produced by the plasma process, Int. J. of
the Phy. Sci., 5 (2010) 5, 535–546
11 P. Gadhari, P. Sahoo, Wear resistance improvement of electroless
Ni–P–Al2O3 composite coating by optimizing process parameters
using taguchi technique, Int. J. of Mater. Chem. and Phy., 1 (2015) 1,
1–10, http:// creativecommons.org/ licenses/by-nc/4.0/
12 M. Yunus, J. F. Rahman, Optimization of usage parameters of cera-
mic coatings in high temperature applications using taguchi design,
Int. J. of Eng. Sci. and Techno., 3 (2011) 8, 6364–6371
13 C. G. Schull, The determination of pore size distribution from gas
adsorption data, J. Am. Chem. Soc ., 70 (1948) 4,1405–1410
D. R. PONNUSAMY RAJARATHNAM, M. JAYARAMAN: INVESTIGATION OF THE WEAR BEHAVIOUR OF AN AISI 1040 ...
944 Materiali in tehnologije / Materials and technology 51 (2017) 6, 939–944
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
945–951
SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU
MAGNESIUM-BASED CAST NANO COMPOSITE VIA NANO-SiO2
ADDITIONS TO THE MELT
SINTEZA IN KARAKTERIZACIJA IN SITU NANOKOMPOZITA NA
OSNOVI MAGNEZIJA Z NANO-SiO2 DODATKOM ZA TALJENJE
Mansour Borouni1, Behzad Niroumand2, Ali Maleki3
1Isfahan University of Technology, Pardis College, Materials Engineering Group, Isfahan 84156-83111, Iran
2Isfahan University of Technology, Department of Mechanical Engineering, Isfahan, 84156-83111, Iran
3Isfahan University of Technology, Research Institute for Steel, Isfahan, 84156-83111, Iran
m.borouni@pa.iut.ac.ir
Prejem rokopisa – received: 2017-04-01; sprejem za objavo – accepted for publication: 2017-05-12
doi:10.17222/mit.2017.036
In this study, AZ91C magnesium matrix in-situ nano-composites reinforced with oxide particles were produced by the addition
of 2 % of mass fractions of silica nanoparticles to the melt using the stir-casting method. For this purpose, nano-silica powder
was mixed in molten AZ91C by a special procedure and stirred for 15 min at 750 °C and cast in a preheated die at 720 °C.
Control samples were also cast under the same conditions. Improved microstructure, reduced porosity and increased hardness,
tensile strength and yield strength of the composite sample were revealed by microstructural and mechanical investigations. The
hardness, yield strength and tensile strength values increased from 65 BHN, 82 MPa and 165 MPa for the monolithic samples to
77 BHN, 97 MPa and 175 MPa for the in-situ formed cast composites. Microstructural and EDS analyses suggested the in-situ
formation of Al2O3, MgAl2O4 and MgO oxide particles by in-situ reaction of the Al, Mg and SiO2 in the melt.
Keywords: AZ91C alloy, in-situ cast nano-composite, silica nanoparticles, mechanical properties
V {tudiji so bili izdelani AZ91C nanokompoziti in situ, na podlagi magnezijeve matrike in oja~ani z oksidnimi delci z dodatkom
2 % nanodelcev silicija za topljenje, z uporabo metode litja z me{anjem. Za ta namen je bil nanosilicijev prah zme{an v
raztopljen AZ91C s posebno metodo in nato 15 min me{an na 750 °C in lit v predogretem modelu na 720 °C. Preizku{anci so
bili ravnotako liti v enakih pogojih. Izbolj{ana mikrostruktura, zmanj{ana poroznost in pove~ana trdota, napetostna trdnost in
napetost vzorcev kompozita so bili odkriti s preiskavami mikrostrukture in z mehanskimi preiskavami. Vrednosti trdote,
napetosti te~enja in natezne napetosti so se pove~ali iz 65 BHN, 82 Mpa in 165 MPa in za monolitne vzorce na 77 BHN, 97
MPa in 175 MPa za in situ formirane lite kompozite. Mikrostrukture in EDS-analize so predlagale in situ formacijo Al2O3,
MgAl2O4 in MgO oksidne delce z in situ reakcijo Al, Mg in SiO2 v topljenem.
Klju~ne besede: AZ91C zlitina, in situ litje nanokompozitov, nanodelci silicija, mehanske lastnosti
1 INTRODUCTION
Besides extensive applications in automobile and
aerospace industries, magnesium and its alloys have had
considerable growth in three markets of communica-
tions, computer and video and photography cameras.
Magnesium is the lightest industrial metal with a density
of 1.74 g/cm3. Magnesium has a high specific strength
and therefore it is used extensively as the metal matrix in
the manufacturing of composites. Among the alloys of
magnesium, Mg-Al-Zn alloys, specifically the AZ91
alloy, have extensive applications in various industries.
Corrosion resistance and relatively high strength are the
particular properties of the AZ91 alloy compared to
other magnesium alloys. The AZ91 alloy is one of the
most common magnesium alloys to produce magne-
sium-matrix composites.1–5
For producing magnesium-matrix composites, rein-
forcing materials with different shapes, sizes and
materials are used. Micron-sized ceramic reinforcements
including carbides, borides and oxides are the most
common.2,5 Various studies are carried out in the field of
magnesium-matrix composites reinforced with ceramic
particles. For instance, in 2008, Hassan and Gupta pro-
duced a magnesium composite reinforced with Al2O3
particles with 0.3-micron sizes using disintegrated melt
deposition method and reported improved yield strength,
tensile strength and flexibility by 2 % of mass fractions
increase of Al2O3 particles.6
By changing the scale of the reinforcing particles
from micrometer to nanometer, their specific surface is
increased significantly and the impact of the properties
of the surface of the particles become more important.
Since one of the mechanisms to increase the properties
of the composites is the load transfer in the interface of
the matrix and reinforcement particles, using nano-
particles, the surface of the reinforcement which is in
contact with the matrix is increased and higher increases
in the properties are expected.7 In a research in 2012,
AZ91D-TiB2 nano-composites were manufactured using
ultrasonic mixing and their sub-structure and mechanical
properties were studied. For AZ91D nano-composites
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 945
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:620.3:621.74:669.721 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)945(2017)
with 2.7 % weight percentage of TiB2 with a mean
diameter of 25 nanometers, the yield strength, ultimate
tensile strength and plasticity were improved by 21 %,
16 %, and 48 %, respectively.8
M. Habibnejad et al.9 studied producing pure magne-
sium and AZ31 magnesium alloy composites using
Al2O3 nano-particles by the stir-casting method.
Characterization of the mechanical properties indicated
that the yield strength and the tensile strength of pure
magnesium and the AZ31 alloy is generally increased
with nano-particles; however, the flexibility decreases.
In most of the researches, including the above-
mentioned studies, the reinforcing particles are placed in
the matrix in an ex-situ procedure. In in-situ composite
fabrication methods, the reinforcing phase is formed
during the procedure with reactions of different ma-
terials. The reaction could take place for a solid powder
or in molten compounds.10
In the current study, the magnesium-matrix nano-
composite AZ91C, reinforced with oxide nano-particles
is produced in in-situ form by adding nano-silica
particles in the molten form and the stir-casting method
and the structural and mechanical properties of the
produced composites are studied.
2 MATERIALS AND METHODS
The standard and measured (by the wet-chemistry
technique) chemical compound of the alloy used in this
study are shown in Table 1.11
Table 1: The chemical compound of the AZ91C alloy used in this
research
% Chemical
composition Standard
11 Measurement
Al 8.1-9.3 8.63
Zn 0.4-1 0.59
Mn 0.13-0.35 0.17
Si 0.3 0.1
Cu 0.1 0.05
Ni 0.01 -
Mg Remained Remained
In this research, silica nano-particles produced from
pyrolysis and burning of HTV silicon polymer are used
for the in-situ production of oxide reinforcing particles.
To produce silica nano-particles, HTV silicon polymer
manufactured by the Korean KCC company is used as
the raw material and the production procedure is
modified as done by M. Senmar et al.12 In this regard, the
required value of the afore-mentioned material is placed
inside the resistance furnace. The furnace is warmed
with a rate of 20 °C/min to reach 700 °C. Then, the
material is maintained at 700 °C to be completely
pyrolyzed and burnt. The resulted product is a white
powder that was analyzed by X-ray diffraction (XRD),
Scanning Electron Microscope (SEM) and Transmission
electron microscopy (TEM). Figure 1, shows the x-ray
diffraction pattern and the images of scanning electron
and transmission electron microscopy.
To make molten AZ91C, first a burner furnace with
natural gas fuel is used for melting the alloy and then a
resistance furnace is used to maintain and control the
temperature. The reason to select this method for melting
the alloy was that the preparation of the molten alloy in
the gas furnace is much quicker than in the resistance
furnace. Therefore, by decreasing the molten alloy pre-
paration time, one could prevent the oxidation of the
molten alloy. As soon as the alloy is melted inside the
gas furnace and for accurately controlling the tempera-
ture, the crucible of the molten alloy is transferred to the
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
946 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: a) XRD pattern12 b) SEM image, c) TEM image 12 from the
powder resulted from pyrolysis and burning of HTV silicon polymer
electric furnace, which is warmed beforehand to reach
the intended temperature and was close to the gas fur-
nace. After reaching the desired temperature, the molten
alloy is mixed. In Figure 2, the schematic picture of the
stir casting system is shown.
To manufacture in-situ magnesium-matrix nano-com-
posites AZ91C reinforced with oxide nano-particles, one
kilograms of AZ91C magnesium bar and 20 g of
nano-silica powder is prepared for each test. Then, holes
with a diameter 13 millimeters are drilled into the mag-
nesium bar. SiO2 nano-powder mixed well with AZ91C
alloy filings was put inside the holes and was pounded
until the holes were filled with AZ91C filings. Then, the
prepared set was put in a graphite crucible inside the
furnace.
Unlike aluminum which has a continuous oxide layer
and the oxide formation on the surface the molten alu-
minum prevents the contact between the molten material
and air, magnesium oxide is porous and cannot make any
protection of the molten material.3,5 In the casting of
magnesium alloy, if the metal and air contact is not cut
during and after the melting, all the magnesium is
oxidized and nothing but a white powder of magnesium
oxide will remain. In stir casting in which the molten
material is turbulent and has more contact with air, this
issue is much more intense. In this study, to protect the
AZ91C molten alloy, a mixture of carbon dioxide and
argon with equal fractions is blown on the surface of the
molten alloy and to mix it, a stirrer made out of simple
carbon steel with three blades with 120° with respect to
each other is used according to Figure 3. The thickness,
width and length of the blades are (2, 15 and 20) mm,
respectively. To increase the mixing power and create a
more downward flow, blades with angles of 45 degrees
were connected with respect to the mixing axis. To keep
the molten alloy clean and increase the lifetime of the
stirrer, the surface of the stirrer is coated with a
nano-ceramic coating. While stirring, the stirrer is inser-
ted into the molten alloy to half the height of the liquid.
After preparing the molten alloy, its temperature is
raised to 750 °C and stirring is done for 15 min with a
speed of 500 min–1 so that the composite slurry is
formed. Then, the temperature of the slurry was de-
creased to 720 °C and was poured into steel molds which
were pre-warmed to 100 °C. The steel mold used which
has four cylindrical holes as well as a cast sample is
illustrated in Figure 4.
It should be noted that three composite samples con-
sisting of 2 % of mass fractions of nano-silica powder
were cast as described above and a non-composite
sample made of AZ91C alloy was cast with similar con-
ditions as the control sample. All the samples were
lathed as the tensile test sample after cleaning based on
ASTM-E8M standard13 according to Figure 5 to inves-
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 947
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: a) Steel mold used in this research, b) A cast sample in the
moldFigure 2: Schematic of the stir-casting system used in this research
Figure 3: The picture of the stirrer used in this research
with 2.7 % weight percentage of TiB2 with a mean
diameter of 25 nanometers, the yield strength, ultimate
tensile strength and plasticity were improved by 21 %,
16 %, and 48 %, respectively.8
M. Habibnejad et al.9 studied producing pure magne-
sium and AZ31 magnesium alloy composites using
Al2O3 nano-particles by the stir-casting method.
Characterization of the mechanical properties indicated
that the yield strength and the tensile strength of pure
magnesium and the AZ31 alloy is generally increased
with nano-particles; however, the flexibility decreases.
In most of the researches, including the above-
mentioned studies, the reinforcing particles are placed in
the matrix in an ex-situ procedure. In in-situ composite
fabrication methods, the reinforcing phase is formed
during the procedure with reactions of different ma-
terials. The reaction could take place for a solid powder
or in molten compounds.10
In the current study, the magnesium-matrix nano-
composite AZ91C, reinforced with oxide nano-particles
is produced in in-situ form by adding nano-silica
particles in the molten form and the stir-casting method
and the structural and mechanical properties of the
produced composites are studied.
2 MATERIALS AND METHODS
The standard and measured (by the wet-chemistry
technique) chemical compound of the alloy used in this
study are shown in Table 1.11
Table 1: The chemical compound of the AZ91C alloy used in this
research
% Chemical
composition Standard
11 Measurement
Al 8.1-9.3 8.63
Zn 0.4-1 0.59
Mn 0.13-0.35 0.17
Si 0.3 0.1
Cu 0.1 0.05
Ni 0.01 -
Mg Remained Remained
In this research, silica nano-particles produced from
pyrolysis and burning of HTV silicon polymer are used
for the in-situ production of oxide reinforcing particles.
To produce silica nano-particles, HTV silicon polymer
manufactured by the Korean KCC company is used as
the raw material and the production procedure is
modified as done by M. Senmar et al.12 In this regard, the
required value of the afore-mentioned material is placed
inside the resistance furnace. The furnace is warmed
with a rate of 20 °C/min to reach 700 °C. Then, the
material is maintained at 700 °C to be completely
pyrolyzed and burnt. The resulted product is a white
powder that was analyzed by X-ray diffraction (XRD),
Scanning Electron Microscope (SEM) and Transmission
electron microscopy (TEM). Figure 1, shows the x-ray
diffraction pattern and the images of scanning electron
and transmission electron microscopy.
To make molten AZ91C, first a burner furnace with
natural gas fuel is used for melting the alloy and then a
resistance furnace is used to maintain and control the
temperature. The reason to select this method for melting
the alloy was that the preparation of the molten alloy in
the gas furnace is much quicker than in the resistance
furnace. Therefore, by decreasing the molten alloy pre-
paration time, one could prevent the oxidation of the
molten alloy. As soon as the alloy is melted inside the
gas furnace and for accurately controlling the tempera-
ture, the crucible of the molten alloy is transferred to the
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
946 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: a) XRD pattern12 b) SEM image, c) TEM image 12 from the
powder resulted from pyrolysis and burning of HTV silicon polymer
electric furnace, which is warmed beforehand to reach
the intended temperature and was close to the gas fur-
nace. After reaching the desired temperature, the molten
alloy is mixed. In Figure 2, the schematic picture of the
stir casting system is shown.
To manufacture in-situ magnesium-matrix nano-com-
posites AZ91C reinforced with oxide nano-particles, one
kilograms of AZ91C magnesium bar and 20 g of
nano-silica powder is prepared for each test. Then, holes
with a diameter 13 millimeters are drilled into the mag-
nesium bar. SiO2 nano-powder mixed well with AZ91C
alloy filings was put inside the holes and was pounded
until the holes were filled with AZ91C filings. Then, the
prepared set was put in a graphite crucible inside the
furnace.
Unlike aluminum which has a continuous oxide layer
and the oxide formation on the surface the molten alu-
minum prevents the contact between the molten material
and air, magnesium oxide is porous and cannot make any
protection of the molten material.3,5 In the casting of
magnesium alloy, if the metal and air contact is not cut
during and after the melting, all the magnesium is
oxidized and nothing but a white powder of magnesium
oxide will remain. In stir casting in which the molten
material is turbulent and has more contact with air, this
issue is much more intense. In this study, to protect the
AZ91C molten alloy, a mixture of carbon dioxide and
argon with equal fractions is blown on the surface of the
molten alloy and to mix it, a stirrer made out of simple
carbon steel with three blades with 120° with respect to
each other is used according to Figure 3. The thickness,
width and length of the blades are (2, 15 and 20) mm,
respectively. To increase the mixing power and create a
more downward flow, blades with angles of 45 degrees
were connected with respect to the mixing axis. To keep
the molten alloy clean and increase the lifetime of the
stirrer, the surface of the stirrer is coated with a
nano-ceramic coating. While stirring, the stirrer is inser-
ted into the molten alloy to half the height of the liquid.
After preparing the molten alloy, its temperature is
raised to 750 °C and stirring is done for 15 min with a
speed of 500 min–1 so that the composite slurry is
formed. Then, the temperature of the slurry was de-
creased to 720 °C and was poured into steel molds which
were pre-warmed to 100 °C. The steel mold used which
has four cylindrical holes as well as a cast sample is
illustrated in Figure 4.
It should be noted that three composite samples con-
sisting of 2 % of mass fractions of nano-silica powder
were cast as described above and a non-composite
sample made of AZ91C alloy was cast with similar con-
ditions as the control sample. All the samples were
lathed as the tensile test sample after cleaning based on
ASTM-E8M standard13 according to Figure 5 to inves-
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 947
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: a) Steel mold used in this research, b) A cast sample in the
moldFigure 2: Schematic of the stir-casting system used in this research
Figure 3: The picture of the stirrer used in this research
tigate the tensile properties. Preparing the sample for
studying the micro-structures was performed according
to the ASTM-E3-01 standard.14 The surfaces of the sam-
ples were prepared in Nital Etch Solution 2 % and their
microstructures were studied using a Mec 1042C light
microscope.
3 RESULTS AND DISCUSSION
3.1 Microstructural studies
Microstructural non-composite (control) and nano-
composites samples are shown in Figure 6 by optical
microscopes. As observed in Figures 6a and 6b, AZ91C
alloy microstructures (control sample) consist of
continuous intermetallic phase 
-Mg17Al12 which has
surrounded the primary magnesium dendrites a–Mg.

-Mg17Al12 phase is mainly distributed along the boun-
daries of the primary phase a–Mg grains and is in the
shape of a long and continuous grid that leads to a
reduction of the mechanical properties.
An important point when studying the nano-com-
posite microstructures is to investigate the distribution
and the bonds of the reinforcing particles in the matrix.
Nevertheless, in Figures 6c and 6d which display the
nano-structures of the composite sample consisting of
2 % of mass fractions of nano-silica particles, there is no
evidence of reinforcing particles in the matrix. Using
nanometric reinforcing materials, when a proper distri-
bution of the particles is achieved in the composite and
large lumps of reinforcing material is not present in the
structure, identifying and finding the reinforcing parti-
cles in the micro-structure is not possible with light
microscopy and electronic microscopies are needed to
study at higher magnifications. Also, indirect observa-
tions and studying the mechanical and physical
properties could lead to understanding the presence and
distribution of the reinforcements in the matrix.
Figure 7 illustrates the Scanning Electron Micro-
scopy (SEM) images for the composite sample consist-
ing of 2 % of mass fractions SiO2 reinforcing nano-parti-
cles. In this picture, particles with dimensions of tens to
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
948 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Scanning electron microscopy (SEM) images for the com-
posite sample consisting of 2 % of mass fractions of SiO2 reinforcing
nano-particles
Figure 6: Light microscopic images in two different magnifications,
a) and b) non-composite cast sample micro-structure, c) and d)
composite cast micro-structure consisting of 2 % of reinforcing SiO2
nano-particles
Figure 5: Schematic of the tensile test sample13
hundreds nanometers are observed. Figure 8 shows the
EDS analysis of the three specified phases of Figure 7c.
According to this analysis, all the observed particles are
oxidized and are made of Al2O3, MgO and MgAl2O4 and
no sign of added nano-silica particles into the structure is
observed. Therefore, it seems that the added nano-silica
particles are reduced in the molten alloy and releasing
oxygen has led to the in-situ creation of new oxide
phases that are studied in what follows.
On the other hand, in Figures 6c and 6d, it is ob-
served that in AZ91C nano-composites, consisting of
oxide nano-particles, the dendrites of the main phase
-Mg have become finer and the shape of the initial
phase has changed to equiaxed dendritic structure from a
coarse dendritic form. It seems that the formed nano-
particles in the molten alloy could have led to finer -Mg
phase by creating the condition for better heterogeneous
nucleation or effective prevention of the growth of
grains, as well as modifying the continuous grids of
phase 
-Mg17Al12.
3.2 Thermodynamic analysis of phase formations in
the Mg-SiO2 system
The chemical compound of the used alloy is
presented in Table 1 in which magnesium is the base
metal and aluminum is the main alloying element.
Moreover, during the procedure, nano-silica particles
with high specific surface areas are added to the molten
alloy at 750 °C, which are expected to create a good
condition for a reaction with the molten alloy. According
Sreekumar et al.,17 reactions 1 to 5 could occur between
the main elements in the molten material and nano-silica
particles. The released energy for each reaction at 750 °C
(1023 K) is also shown next to each of them in Tab-
le 2.15–17
Since the released energy of all of these reactions is
extremely negative at 750 °C, formation of Al2O3,
MgAl2O4 and MgO phases, which are shown in Figure
7c, are thermodynamically feasible and spontaneous.
The MgAl2O4 phase shows a combination of unique pro-
perties such as low electrical conductivity, low thermal
expansion coefficient, good thermal shock resistance, low
dielectric constant, high electrical resistance, high melt-
ing point (2135 °C) and high mechanical strength.17,18
Moreover, this compound has a good adhesion to metal
matrices.19 Various studies are carried out regarding the
formation, interface type and crystallography of the
MgAl2O4 phase with reinforcements used in metal-
matrix composites. The oxide reinforcements were used
such as Al2O3, Saffil, Mullite, Kaowool, Al4B3O18, MgO,
ASZ (Composition Al2O3, SiO2 and ZrO2 in 3 : 5 : 2 ratio
and are amorphous in their as-fabricated state) and glass
fibers or non-oxide reinforcements such as graphite,
B4C, AlN and SiC. Studying the reactions with oxide
reinforcements has shown that MgAl2O4 is formed due to
the reaction of the oxide reinforcements with aluminum
and magnesium in the matrix alloy. Also, the oxidation
of the volatile surface of non-oxide reinforcements leads
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 949
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 8: EDS elemental analysis from points a, b, and c
Table 2: Reactions could occur between the main elements in the molten material and nano-silica particles
(1) G01023 K = -348.19 kJ/mol 4Mg(l)+SiO2(s)  Mg2Si(s)+2MgO(s)
(2) G01023 K = -268.22 kJ/mol SiO2(s)+2Mg(l)  2MgO(s)+Si(l)
(3) G01023 K = -449.63 kJ/mol 2SiO2(s)+Mg(l)+2Al(l)  MgAl2O4(s)+2Si(l)
(4) G01023 K = -556.44 kJ/mol 3SiO2(s)+4Al(l)  2Al2O3(s)+3Si(l)
(5) G01023 K = -631.08 kJ/mol 3SiO2(s)+2MgO(s)+4Al(l)  2MgAl2O4(s)+3Si(l)
tigate the tensile properties. Preparing the sample for
studying the micro-structures was performed according
to the ASTM-E3-01 standard.14 The surfaces of the sam-
ples were prepared in Nital Etch Solution 2 % and their
microstructures were studied using a Mec 1042C light
microscope.
3 RESULTS AND DISCUSSION
3.1 Microstructural studies
Microstructural non-composite (control) and nano-
composites samples are shown in Figure 6 by optical
microscopes. As observed in Figures 6a and 6b, AZ91C
alloy microstructures (control sample) consist of
continuous intermetallic phase 
-Mg17Al12 which has
surrounded the primary magnesium dendrites a–Mg.

-Mg17Al12 phase is mainly distributed along the boun-
daries of the primary phase a–Mg grains and is in the
shape of a long and continuous grid that leads to a
reduction of the mechanical properties.
An important point when studying the nano-com-
posite microstructures is to investigate the distribution
and the bonds of the reinforcing particles in the matrix.
Nevertheless, in Figures 6c and 6d which display the
nano-structures of the composite sample consisting of
2 % of mass fractions of nano-silica particles, there is no
evidence of reinforcing particles in the matrix. Using
nanometric reinforcing materials, when a proper distri-
bution of the particles is achieved in the composite and
large lumps of reinforcing material is not present in the
structure, identifying and finding the reinforcing parti-
cles in the micro-structure is not possible with light
microscopy and electronic microscopies are needed to
study at higher magnifications. Also, indirect observa-
tions and studying the mechanical and physical
properties could lead to understanding the presence and
distribution of the reinforcements in the matrix.
Figure 7 illustrates the Scanning Electron Micro-
scopy (SEM) images for the composite sample consist-
ing of 2 % of mass fractions SiO2 reinforcing nano-parti-
cles. In this picture, particles with dimensions of tens to
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
948 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Scanning electron microscopy (SEM) images for the com-
posite sample consisting of 2 % of mass fractions of SiO2 reinforcing
nano-particles
Figure 6: Light microscopic images in two different magnifications,
a) and b) non-composite cast sample micro-structure, c) and d)
composite cast micro-structure consisting of 2 % of reinforcing SiO2
nano-particles
Figure 5: Schematic of the tensile test sample13
hundreds nanometers are observed. Figure 8 shows the
EDS analysis of the three specified phases of Figure 7c.
According to this analysis, all the observed particles are
oxidized and are made of Al2O3, MgO and MgAl2O4 and
no sign of added nano-silica particles into the structure is
observed. Therefore, it seems that the added nano-silica
particles are reduced in the molten alloy and releasing
oxygen has led to the in-situ creation of new oxide
phases that are studied in what follows.
On the other hand, in Figures 6c and 6d, it is ob-
served that in AZ91C nano-composites, consisting of
oxide nano-particles, the dendrites of the main phase
-Mg have become finer and the shape of the initial
phase has changed to equiaxed dendritic structure from a
coarse dendritic form. It seems that the formed nano-
particles in the molten alloy could have led to finer -Mg
phase by creating the condition for better heterogeneous
nucleation or effective prevention of the growth of
grains, as well as modifying the continuous grids of
phase 
-Mg17Al12.
3.2 Thermodynamic analysis of phase formations in
the Mg-SiO2 system
The chemical compound of the used alloy is
presented in Table 1 in which magnesium is the base
metal and aluminum is the main alloying element.
Moreover, during the procedure, nano-silica particles
with high specific surface areas are added to the molten
alloy at 750 °C, which are expected to create a good
condition for a reaction with the molten alloy. According
Sreekumar et al.,17 reactions 1 to 5 could occur between
the main elements in the molten material and nano-silica
particles. The released energy for each reaction at 750 °C
(1023 K) is also shown next to each of them in Tab-
le 2.15–17
Since the released energy of all of these reactions is
extremely negative at 750 °C, formation of Al2O3,
MgAl2O4 and MgO phases, which are shown in Figure
7c, are thermodynamically feasible and spontaneous.
The MgAl2O4 phase shows a combination of unique pro-
perties such as low electrical conductivity, low thermal
expansion coefficient, good thermal shock resistance, low
dielectric constant, high electrical resistance, high melt-
ing point (2135 °C) and high mechanical strength.17,18
Moreover, this compound has a good adhesion to metal
matrices.19 Various studies are carried out regarding the
formation, interface type and crystallography of the
MgAl2O4 phase with reinforcements used in metal-
matrix composites. The oxide reinforcements were used
such as Al2O3, Saffil, Mullite, Kaowool, Al4B3O18, MgO,
ASZ (Composition Al2O3, SiO2 and ZrO2 in 3 : 5 : 2 ratio
and are amorphous in their as-fabricated state) and glass
fibers or non-oxide reinforcements such as graphite,
B4C, AlN and SiC. Studying the reactions with oxide
reinforcements has shown that MgAl2O4 is formed due to
the reaction of the oxide reinforcements with aluminum
and magnesium in the matrix alloy. Also, the oxidation
of the volatile surface of non-oxide reinforcements leads
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 949
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 8: EDS elemental analysis from points a, b, and c
Table 2: Reactions could occur between the main elements in the molten material and nano-silica particles
(1) G01023 K = -348.19 kJ/mol 4Mg(l)+SiO2(s)  Mg2Si(s)+2MgO(s)
(2) G01023 K = -268.22 kJ/mol SiO2(s)+2Mg(l)  2MgO(s)+Si(l)
(3) G01023 K = -449.63 kJ/mol 2SiO2(s)+Mg(l)+2Al(l)  MgAl2O4(s)+2Si(l)
(4) G01023 K = -556.44 kJ/mol 3SiO2(s)+4Al(l)  2Al2O3(s)+3Si(l)
(5) G01023 K = -631.08 kJ/mol 3SiO2(s)+2MgO(s)+4Al(l)  2MgAl2O4(s)+3Si(l)
to the formation of a reactive oxide layer, which helps
the formation of MgAl2O4. The formation of SiO2 on
SiC, Al2O3 on AlN and B2O3 on B4C are the examples of
this mechanism.17 In some cases it is reported that the
absorption of the oxygen on the surface of the
reinforcements acts as a source for the formation of
MgAl2O4.19 Al2O3 has rigidity and high strength as well
as corrosion resistance and sufficient thermal stability.20
Magnesium composites reinforced with Al2O3
nano-particles show a considerable increase in the
microhardness and a slight increase in the elasticity
modulus and yield strength.21 The hardness and tensile
strength increase in the AZ91 alloy reinforced with
MgO.22
3.3 Investigating the mechanical properties
Figure 9 shows an example of stress-strain curves
resulting from the tensile test for composite and non-
composite samples. The average values of the mechani-
cal properties including hardness, yield strength, ultimate
tensile strength and elongation percentage of the non-
composite sample and nano-composite samples are
shown in Table 3.
As observed in Figure 9 and Table 3, hardness, yield
strength and ultimate tensile strength of the cast nano-
composite samples increased compared to the cast non-
composite sample (control sample) and their elongation
percentage has slightly decreased.
Different mechanisms are presented for improving
the mechanical properties of the metal-matrix compo-
sites. Examining the shapes and sizes of the grains and
the properties of the composite samples, one could
understand the effectiveness of the operation. One of the
evidences of the improvement of the properties in the
composite samples is that the microstructures of the cast
nano-composite samples have finer and more uniform
grains compared to the non-composite samples (Hall-
Petch effect). Also, the secondary phase -Mg17Al12 is
considerably crushed in the grain boundaries of the
primary phase, has lost its continuity and is distributed
more uniformly in the structure. It seems that the reason
for this is the uniform distribution of the reinforcing
particles in the structure and their effect on the
nucleation of the primary phase and preventing the
growth of the grains. Another impact is the formation of
oxide nano-particles in the matrix such that they are
almost homogeneously distributed in the matrix. As
observed in Figure 6, the distribution and how the
reinforcing nano-particles are put together are not clear
in this picture, which shows the relatively proper distri-
bution of the reinforcing particles and the absence of
large lumps in the matrix.
A. Sanati Zadeh et al.23 found the Hall-Petch
strengthening effect to be very important for the strength
of nano-composites such that it causes up to 50 % of the
total strengthening.
As the elasticity modulus of the matrix and reinforce-
ment are completely different, when one-dimensional
loading is applied on a composite material, a combined
stress distribution is formed. Highly accurate analyses
show that shear stresses occur in the boundary of the
matrix with the particles, which leads to an increased
strength.24
As shown in Figure 8 and Table 3, while the
strengths of the composite samples are increased, their
elongation percentages are somewhat decreased. This is
generally observed in composites. In fact, the same
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
950 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 9: An example of stress-strain curves resulted from tensile test
for: a) non-composite samples, b) composite samples
Table 3: Mechanical properties of non-composite and nano-composite samples
% Nano silica Hardness (BHN) U.T.S (MPa) Y.S (MPa) % El
0 5±65 3±165 2±82 0.3±3.5 Non-composite sample (control sample)
2 3±77 2±175 3±97 0.2±3 Nano-composite sample (average of threetests)
- +18.5 +6.1 +18.3 -14.3 Percent change
mechanisms which lead to an increased strength,
decrease the deformation of the matrix as well. More-
over, the weak bond between the reinforcing particles
and magnesium matrix and defects such as gaseous pores
could also be factoring, which leads to a more intense
decrease of the flexibility of the composites.
4 CONCLUSION
An AZ91C nano-composite consisting of Al2O3,
MgAl2O4 and MgO oxide nano-particles is successfully
produced using the stir-casting method. The existence of
Al2O3, MgAl2O4 and MgO oxide particles in an AZ91C
alloy has a proper reinforcing role and the manufactured
nano-composites have finer and more uniform grains
compared to the non-composite control sample. Also, the
secondary phase 
-Mg17Al12 is fairly crushed and is
distributed in a non-continuous form in the structure.
These changes lead to the improvement of the mecha-
nical properties compared to the non-composite control
sample so that the hardness, yield strength and tensile
strength are increased from 65 BHN, 82 MPa and 165
MPa in the non-composite sample to 77 BHN, 97 MPa
and 175 MPa in the composite sample.
Acknowledgements
The authors are grateful for support of this research
by Isfahan University of Technology (IUT).
5 REFERENCES
1 E. F. Horst, L. M. Barry, Magnesium Technology (Metallurgy,
Design Data, Applications), Springer, Germany, (2006)
2 M. Gupta, N. M. L. Sharon, Magnesium, Magnesium Alloys, and
Magnesium Composites, John Wiley & Sons, Inc., New Jersey,
(2011)
3 A. W. Brace, F. A. Allen, Magnesium Casting Technology, London,
Chapman & Hall; New York, Reinhold Pub. Corp., (1957)
4 ASM Handbook Committee, Metals Handbook, Vol. 15, casting,
ASM International, Ten Edition, (2008)
5 H. E. Friedrich, B. L. Mordike, Magnesium Technology (Metallurgy,
Design Data, Applications), 1st Ed., Springer, Germany, (2006)
6 S. F. Hassan, M. Gupta, Effect of submicron size Al2O3 particulates
on microstructural and tensile properties of elemental Mg. Journal of
Alloys and Compounds, 457 (2008), 244–250, doi:10.1016/
j.jallcom.2007.03.058
7 D. Vollath, Nanomaterials: Nanomaterials: An Introduction to
Synthesis, Properties and Applications, 2nd Edition, (2013)
8 H. Choi, Y. Sun, B. P. Slater, H. Konishi, X. Li, AZ91D-TiB2 Nano-
composites Fabricated by Solidification Nanoprocessing, Advanced
Engineering Materiales, 14 (2012) 5, 291–295, doi:10.1002/adem.
201100313
9 M. Habibnejad-Korayem, R. Mahmudi, W. J. Poole, Enhanced
properties of Mg-based nanocomposites reinforced with Al2O3 nano
particles, Materials Science and Engineering A, 519 (2009),
198–203, doi:10.1016/j.msea.2009.05.001
10 K. Kainer, Metal matrix composite, Wiley book, (2006)
11 International ASTM B 80-05, Standard specification for magnesium
–alloy sand casting, (2005)
12 M. Senemar, A. Maleki, B. Niroumand, A. Allafchian, A Novel And
Facile Method For Silica Nanoparticles Synthesis From High
Temperature Vulcanization (HTV) Silicone, Association of
Metallurgical Engineers of Serbia (AMES), 22 (2016) 1, 1–8,
https://metall-mater-eng.com/index.php/home/article/view/134/120
13 International ASTM B E8/E8M – 09, Standard Test Methods for
Tension Testing of Metallic Materials1, (2010)
14 International ASTM E03-1, Standard Practice for Preparation of
Metallographic Specimens, (2007)
15 D. Huang, Y. Wang, Y. Wang, H. Cui, X. Guo, In situ Mg2Si rein-
forced Mg alloy synthesized in Mg-SiO2 system, Advanced Materials
Research, 146–147 (2011), 1775–1779, doi:10.4028/www.scien-
tific.net/AMR.146-147.1775
16 Y. J. Liang, Y. C. Chen, Thermodynamic Data Handbook on Inor-
ganic Substances, Dongbei University Press, China, in Chinese,
(1993)
17 V. M. Sreekumar, R. M. Pillai, B. C. Pai, M. Chakraborty, Evolution
of MgAl2O4 crystals in Al-Mg-SiO2 composites, Applied Physics A
Materials Science & Processing, A 90 (2008), 745–752, doi:10.1007/
s00339-007-4357-2
18 C. Pacurariu, I. Lazau, Z. Ecsedi, R. Lazau, P. Barvinschi, G. Margi-
nean, New synthesis methods of MgAl2O4 spinel, Journal of the
European Ceramic Society, 27 (2007), 707–710, doi:10.1016/
j.jeurceramsoc.2006.04.050
19 G. Ramani, R. M. Pillai, B. C. Pai, T. R. Ramamohan, Factors affect-
ing the stability of non-wetting dispersed suspensions in metallic
melts, Composites, 22 (1991) 2, 143–150, doi:10.1016/0010-
4361(91)90673-5
20 A. Kazunori, Y. Hiroyuki, Effects of Particle-Dispersion on the
Strength of an Alumina Fiber-Reinforced Aluminum Alloy Matrix
Composite, Materials Transactions, 44 (2003) 6, 1172–1180,
https://www.jim.or.jp/journal/e/pdf3/44/06/1172.pdf
21 T. S. Srivatsan, C. Godbole, T. Quick, M. Paramsothy, M. Gupta,
Mechanical Behavior of a Magnesium Alloy Nanocomposite Under
Conditions of Static Tension and Dynamic Fatigue, Journal of
Materials Engineering and Performance, 22 (2013), 439–453,
doi:10.1007/s11665-012-0276-2
22 Z. Song-li, Z. Yu-tao, C. Gang, In situ (Mg2Si+MgO)/Mg composites
fabricated from AZ91-Al2(SiO3)3 with assistance of high-energy
ultrasonic field, Transactions of Nonferrous metals Society of china,
20 (2010), 2096–2099, doi:10.1016/S1003-6326(09)60424-6
23 A. Sanaty-Zadeh, P. K. Rohatgi, Comparison between Current
Models for the Strength of Particulate Reinforced Metal Matrix
Nanocomposites with Emphasis on Consideration of Hall–Petch
Effect, Materials Science and Engineering, A 531(2012), 112–118,
doi:10.1016/j.msea.2011.10.043
24 G. E. Dieter, Mechanical Metallurgy, MacGraw-Hill Book Company
Limited, UK, (1988)
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951 951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
to the formation of a reactive oxide layer, which helps
the formation of MgAl2O4. The formation of SiO2 on
SiC, Al2O3 on AlN and B2O3 on B4C are the examples of
this mechanism.17 In some cases it is reported that the
absorption of the oxygen on the surface of the
reinforcements acts as a source for the formation of
MgAl2O4.19 Al2O3 has rigidity and high strength as well
as corrosion resistance and sufficient thermal stability.20
Magnesium composites reinforced with Al2O3
nano-particles show a considerable increase in the
microhardness and a slight increase in the elasticity
modulus and yield strength.21 The hardness and tensile
strength increase in the AZ91 alloy reinforced with
MgO.22
3.3 Investigating the mechanical properties
Figure 9 shows an example of stress-strain curves
resulting from the tensile test for composite and non-
composite samples. The average values of the mechani-
cal properties including hardness, yield strength, ultimate
tensile strength and elongation percentage of the non-
composite sample and nano-composite samples are
shown in Table 3.
As observed in Figure 9 and Table 3, hardness, yield
strength and ultimate tensile strength of the cast nano-
composite samples increased compared to the cast non-
composite sample (control sample) and their elongation
percentage has slightly decreased.
Different mechanisms are presented for improving
the mechanical properties of the metal-matrix compo-
sites. Examining the shapes and sizes of the grains and
the properties of the composite samples, one could
understand the effectiveness of the operation. One of the
evidences of the improvement of the properties in the
composite samples is that the microstructures of the cast
nano-composite samples have finer and more uniform
grains compared to the non-composite samples (Hall-
Petch effect). Also, the secondary phase -Mg17Al12 is
considerably crushed in the grain boundaries of the
primary phase, has lost its continuity and is distributed
more uniformly in the structure. It seems that the reason
for this is the uniform distribution of the reinforcing
particles in the structure and their effect on the
nucleation of the primary phase and preventing the
growth of the grains. Another impact is the formation of
oxide nano-particles in the matrix such that they are
almost homogeneously distributed in the matrix. As
observed in Figure 6, the distribution and how the
reinforcing nano-particles are put together are not clear
in this picture, which shows the relatively proper distri-
bution of the reinforcing particles and the absence of
large lumps in the matrix.
A. Sanati Zadeh et al.23 found the Hall-Petch
strengthening effect to be very important for the strength
of nano-composites such that it causes up to 50 % of the
total strengthening.
As the elasticity modulus of the matrix and reinforce-
ment are completely different, when one-dimensional
loading is applied on a composite material, a combined
stress distribution is formed. Highly accurate analyses
show that shear stresses occur in the boundary of the
matrix with the particles, which leads to an increased
strength.24
As shown in Figure 8 and Table 3, while the
strengths of the composite samples are increased, their
elongation percentages are somewhat decreased. This is
generally observed in composites. In fact, the same
M. BOROUNI et al.: SYNTHESIS AND CHARACTERIZATION OF AN IN-SITU MAGNESIUM-BASED ...
950 Materiali in tehnologije / Materials and technology 51 (2017) 6, 945–951
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 9: An example of stress-strain curves resulted from tensile test
for: a) non-composite samples, b) composite samples
Table 3: Mechanical properties of non-composite and nano-composite samples
% Nano silica Hardness (BHN) U.T.S (MPa) Y.S (MPa) % El
0 5±65 3±165 2±82 0.3±3.5 Non-composite sample (control sample)
2 3±77 2±175 3±97 0.2±3 Nano-composite sample (average of threetests)
- +18.5 +6.1 +18.3 -14.3 Percent change
mechanisms which lead to an increased strength,
decrease the deformation of the matrix as well. More-
over, the weak bond between the reinforcing particles
and magnesium matrix and defects such as gaseous pores
could also be factoring, which leads to a more intense
decrease of the flexibility of the composites.
4 CONCLUSION
An AZ91C nano-composite consisting of Al2O3,
MgAl2O4 and MgO oxide nano-particles is successfully
produced using the stir-casting method. The existence of
Al2O3, MgAl2O4 and MgO oxide particles in an AZ91C
alloy has a proper reinforcing role and the manufactured
nano-composites have finer and more uniform grains
compared to the non-composite control sample. Also, the
secondary phase 
-Mg17Al12 is fairly crushed and is
distributed in a non-continuous form in the structure.
These changes lead to the improvement of the mecha-
nical properties compared to the non-composite control
sample so that the hardness, yield strength and tensile
strength are increased from 65 BHN, 82 MPa and 165
MPa in the non-composite sample to 77 BHN, 97 MPa
and 175 MPa in the composite sample.
Acknowledgements
The authors are grateful for support of this research
by Isfahan University of Technology (IUT).
5 REFERENCES
1 E. F. Horst, L. M. Barry, Magnesium Technology (Metallurgy,
Design Data, Applications), Springer, Germany, (2006)
2 M. Gupta, N. M. L. Sharon, Magnesium, Magnesium Alloys, and
Magnesium Composites, John Wiley & Sons, Inc., New Jersey,
(2011)
3 A. W. Brace, F. A. Allen, Magnesium Casting Technology, London,
Chapman & Hall; New York, Reinhold Pub. Corp., (1957)
4 ASM Handbook Committee, Metals Handbook, Vol. 15, casting,
ASM International, Ten Edition, (2008)
5 H. E. Friedrich, B. L. Mordike, Magnesium Technology (Metallurgy,
Design Data, Applications), 1st Ed., Springer, Germany, (2006)
6 S. F. Hassan, M. Gupta, Effect of submicron size Al2O3 particulates
on microstructural and tensile properties of elemental Mg. Journal of
Alloys and Compounds, 457 (2008), 244–250, doi:10.1016/
j.jallcom.2007.03.058
7 D. Vollath, Nanomaterials: Nanomaterials: An Introduction to
Synthesis, Properties and Applications, 2nd Edition, (2013)
8 H. Choi, Y. Sun, B. P. Slater, H. Konishi, X. Li, AZ91D-TiB2 Nano-
composites Fabricated by Solidification Nanoprocessing, Advanced
Engineering Materiales, 14 (2012) 5, 291–295, doi:10.1002/adem.
201100313
9 M. Habibnejad-Korayem, R. Mahmudi, W. J. Poole, Enhanced
properties of Mg-based nanocomposites reinforced with Al2O3 nano
particles, Materials Science and Engineering A, 519 (2009),
198–203, doi:10.1016/j.msea.2009.05.001
10 K. Kainer, Metal matrix composite, Wiley book, (2006)
11 International ASTM B 80-05, Standard specification for magnesium
–alloy sand casting, (2005)
12 M. Senemar, A. Maleki, B. Niroumand, A. Allafchian, A Novel And
Facile Method For Silica Nanoparticles Synthesis From High
Temperature Vulcanization (HTV) Silicone, Association of
Metallurgical Engineers of Serbia (AMES), 22 (2016) 1, 1–8,
https://metall-mater-eng.com/index.php/home/article/view/134/120
13 International ASTM B E8/E8M – 09, Standard Test Methods for
Tension Testing of Metallic Materials1, (2010)
14 International ASTM E03-1, Standard Practice for Preparation of
Metallographic Specimens, (2007)
15 D. Huang, Y. Wang, Y. Wang, H. Cui, X. Guo, In situ Mg2Si rein-
forced Mg alloy synthesized in Mg-SiO2 system, Advanced Materials
Research, 146–147 (2011), 1775–1779, doi:10.4028/www.scien-
tific.net/AMR.146-147.1775
16 Y. J. Liang, Y. C. Chen, Thermodynamic Data Handbook on Inor-
ganic Substances, Dongbei University Press, China, in Chinese,
(1993)
17 V. M. Sreekumar, R. M. Pillai, B. C. Pai, M. Chakraborty, Evolution
of MgAl2O4 crystals in Al-Mg-SiO2 composites, Applied Physics A
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